Back to EveryPatent.com
| United States Patent |
5,541,704
|
|
Dunsmore
|
July 30, 1996
|
Camera with LED photometer
Abstract
A camera including a photoelectric diode operated as an emitter in a first
mode and a sensor in a second mode. The camera includes a first circuit
that operates the diode to emit visible radiation and a second circuit
that operates the diode to sense scene illumination. The diode is switched
between the respective circuits selectively to operate in its first and
second modes. The first circuit preferably is a timing circuit in a
self-timing camera, but also might provide other functions including
reduction of red-eye effects. The second circuit preferably is a
photometer for controlling exposure.
| Inventors:
|
Dunsmore; Clay A. (Fairport, NY)
|
| Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
| Appl. No.:
|
287431 |
| Filed:
|
August 8, 1994 |
| Current U.S. Class: |
396/158; 396/213; 396/268 |
| Intern'l Class: |
G03B 007/00; G03B 007/099 |
| Field of Search: |
354/476,410,403,409,471
257/80,84
|
References Cited
U.S. Patent Documents
| 4460259 | Jul., 1984 | Greivenkamp, Jr. et al. | 354/403.
|
| 4485391 | Nov., 1984 | Poulain et al. | 357/19.
|
| 4534638 | Aug., 1985 | Hirohata et al.
| |
| 4561752 | Dec., 1985 | Miyamoto et al.
| |
| 4564756 | Jan., 1986 | Johnson.
| |
| 5109248 | Apr., 1992 | Petrakos et al.
| |
| 5408092 | Apr., 1995 | Maurice et al. | 250/227.
|
| Foreign Patent Documents |
| 2207500 | Feb., 1989 | GB.
| |
Primary Examiner: Gellner; Michael L.
Assistant Examiner: Miller; Matthew
Attorney, Agent or Firm: Mathews; J. Addison, Howley; David A.
Claims
What is claimed is:
1. A photographic camera including an optical system for focusing scene
illumination on an exposure plane, said camera comprising:
a photometer circuit including a light emitting diode electrically coupled
as a sensor in said circuit and disposed on said camera for sensing said
scene illumination, said light emitting diode not emitting light when
electrically coupled as a sensor in said circuit; and
a switch for making and breaking said electrical coupling of said light
emitting diode in said photometer circuit.
2. The invention of claim 1, including a second circuit and a switch for
alternately coupling said light emitting diode electrically in said
photometer circuit and said second circuit, respectively.
3. The invention of claim 1, including a timing circuit, and a switch for
alternately coupling said light emitting diode electrically in said
photometer circuit and said timing circuit, respectively, said photometer
circuit biasing said light emitting diode as a sensor, and said timing
circuit biasing said light emitting diode as an emitter.
4. A photographic camera comprising:
a diode encased in light transmissive material;
a first circuit operating said diode as a photoemitter;
a second circuit operating said diode as a photosensor; and,
means for selectively coupling said diode to said first and second
circuits, respectively.
5. The invention of claim 4, wherein said camera records images of a scene,
and said diode is disposed for receiving illumination from the scene.
6. The invention of claim 5, wherein said second circuit is a photometer
for setting a camera exposure variable.
7. The invention of claim 6, wherein said first circuit includes means
using said diode to indicate a condition of said first circuit.
8. A camera for recording images of a scene and including an optical system
for focusing the scene at an image plane, said camera comprising:
a diode disposed on said camera for receiving illumination from the scene;
a first circuit operating said diode as a photoemitter and including means
for selectively energizing said diode to indicate a condition of said
circuit;
a second circuit operating said diode as a photosensor and including means
using electrical output of said diode as a photometer for sensing
intensity of the scene illumination, said diode not emitting light when
being operated as a photosensor, wherein said first circuit is a timing
circuit, said camera includes an exposure controlling mechanism, and said
second circuit is coupled to said mechanism for adjusting said mechanism
according to said intensity.
9. A camera for recording images of a scene, the camera including an
optical system for focusing illumination from the scene at an image plane,
and an exposure mechanism for controlling intensity of the illumination at
said image plane, said camera comprising:
a diode disposed on said camera for receiving illumination from the scene;
a first circuit operating said diode as a photoemitter and including means
for selectively energizing said diode to emit visible radiation from said
diode;
a photometer operating said diode as a photosensor for sensing said
intensity and including means using the electrical output of said diode
for controlling said mechanism, said diode not emitting visible radiation
when being operated as a photosensor, wherein said first circuit is a
timing circuit and said energizing means energizes said diode to indicate
a timing condition.
10. The invention of claim 9, wherein said first circuit is controlled to
emit radiation from said diode before an exposure to reduce red-eye.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to photometers in photographic cameras, and more
specifically to cameras including optoelectronic elements for sensing
light and emitting light.
2. Description of the Prior Art
Modern cameras frequently include numerous features that are automated for
ease of use and designed for low cost with high quality. Perhaps most
pertinent to the present invention are such features that employ
photoelectronic devices typically falling into two categories. One
category includes light emitters, such as light emitting diodes, that
might be used as indicators or sources of illumination. The other includes
light sensors, such as a photocells, that respond to light intensity.
A known example in the first category is a self-portrait timing circuit.
The camera operator initiates a time-out cycle, delaying the exposure. The
operator then has time to join the scene that is photographed. A light
emitting diode (LED) usually is employed on the front of the camera to
indicate the condition or state of the time-out cycle. In many designs,
the LED blinks at a rate depending on the time remaining in the cycle.
Another example, still in the first category, is a light emitting diode
(LED) employed for reducing a phenomenon known as "red eye." Flash
reflections from the subjects retina produce red spots in the printed
image. An LED, again on the front of the camera, is energized under low
light conditions when a subjects pupils normally would be dilated and
particularly subject to the red eye phenomena. The LED is energized
immediately before the exposure, constricting the subjects pupils, and
reducing red eye. In this example the emitter is used for illumination.
A known example in the second category is a photometer employing a
photocell that senses the level of scene illumination and adjusts the
camera for proper exposure. Other examples sense energy from electronic
flash devices and quench the flash to control the exposure.
Features in the above described two categories often are combined on the
same camera, or have common elements employed for both emitting and
sensing radiation. A single power source might be used, for example, to
drive or bias light emitting and light sensing devices. U.S. Pat. No.
4,460,259 discloses an example of a common element, a lens, that is used
for directing light toward a subject and also for focusing light returned
from the subject. The common lens is used with a light emitting element
and a light sensing element in a triangulation rangefinder.
PROBLEM SOLVED BY THE INVENTION
Although common elements like batteries and lenses have been used in camera
emitting and sensing circuits, separate optoelectronic devices have been
required for light emission and light sensing. This adds to the number of
required components, increasing camera cost and complexity.
Devices designed for sensing light intensity typically are more expensive
than light emitters, especially light emitting diodes (LEDs). Their
addition to camera sensing circuits has a significant cost impact,
particularly in models designed for markets demanding low price.
In addition to cost and complexity, photoelectronic devices are relatively
large compared to other electronic devices. Duplication of such elements
complicates small camera design.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems
set forth above, while also providing advantageous features at reduced
cost and complexity. Briefly summarized, according to one aspect of the
invention, a camera includes a photoelectronic device operated as an
emitter in a first mode and a sensor in a second mode. More specifically,
the camera includes a first circuit that operates a diode to emit visible
radiation and a second circuit that operates the diode to sense scene
illumination. The diode is switched between the respective circuits
selectively to operate in its first and second modes.
According to more specific features, the diode is disposed on the camera
for receiving illumination from the photographic scene. A first circuit
operates the diode as a photoemitter and selectively energizes the diode
to emit radiation. A second circuit operates the diode as a photosensor,
selectively sensing the intensity of light from the scene and using the
electrical output of the diode for controlling the exposure.
The invention has particular utility in cameras where the light sensing and
emitting elements face in the same direction. The first circuit preferably
uses the diode as an indicator in a timer for self portraits, or for
preflash illumination to reduce red-eye. The second circuit preferably is
a photometer for controlling the camera exposure mechanism or an
electronic flash. The light sensing and light emitting elements in such
circuits typically face forward. Of course other applications of the
invention might use reflecting surfaces for redirecting the sensed and
emitted radiation.
The invention reduces the number of parts, the cost and the complexity of
photographic cameras that include light emitting and light sensing
functions.
These and other features and advantages of the invention will be more
clearly understood and appreciated from a review of the following detailed
description of the preferred embodiments and appended claims, and by
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a circuit in a photographic camera according
to a preferred embodiment of the invention, including a photoelectronic
device used in light sensing and light emitting circuits.
FIG. 2 is a schematic view corresponding to part of FIG. 1, depicting the
light emitting function.
FIG. 3 is a schematic view corresponding to part of FIG. 1, depicting the
light sensing function.
FIG. 4 is a schematic perspective view of a camera including the circuit of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to a preferred embodiment of the invention, and to FIGS. 1-4,
a photographic camera 10 is depicted including an optoelectronic device
12, a first circuit 14 operating device 12 as an emitter, and a second
circuit 16 operating device 12 as a sensor. In this preferred embodiment,
and as will become apparent from the following description, optoelectronic
device 12 is used alternately as an emitter in a timing circuit and as a
sensor in a photometer circuit. The timing circuit is depicted
schematically in FIG. 2. The photometer circuit is depicted schematically
in FIG. 3. FIG. 1 represents a combination of FIGS. 2 and 3, including
appropriate switching elements for alternatively configuring the timing
and photometer circuits. FIG. 4 presents a camera incorporating the
circuits.
Camera 10 includes appropriate structure and mechanisms for recording
images of a scene on a photosensitive medium. The camera is illustrated
for purposes of this description with an optical and exposure system 18;
an electronic flash device 20, including a photoflash tube 22; a
viewfinder 24; and a shutter release 26. Optical and exposure system 18
focuses an image of a scene onto an image plane that supports the
photosensitive medium, and controls the exposure. Flash device 20 provides
supplemental artificial illumination and is selectively actuated to flash
when needed. Viewfinder 24 is an aid for pointing the camera, and shutter
release 26 initiates the exposure and flash sequences in proper timed
relation with other camera functions. Although the camera 10 is intended
for relatively low cost applications, it has numerous automated features
including automatic exposure control and flash quenching. Such features
are provided by commercial mechanisms widely available and known to those
skilled in the art.
The camera further includes a timing device for self portraits. Actuation
of switch 28 initiates a time-out sequence that delays the exposure for a
predetermined time interval during which the camera operator can join the
scene to be photographed. An indicator 30, visible from the front of the
camera, provides notification that the timing device is active. When the
time-out sequence is completed, the camera is actuated by the timing
mechanism to initiate the exposure sequence in the normal manor.
Electrical components of the timing device (FIG. 2) include optoelectronic
device 12, transistor 34, battery 36 and resistor 38. The optoelectronic
device 12 is a light emitting diode (LED) 40 encased in transmissive
material that is the indicator 30 in FIG. 4. When switch 28 is closed to
initiate the timing sequence, it turns on transistor 34 allowing current
from battery 36 to flow through resistor 38 and the light emitting diode
(LED) 40. In this mode of operation, the LED is forward biased and emits
light in the visible spectrum to indicate the on or off condition of the
timing circuit. Since the LED is visible from the front of the camera, at
indicator 30, the operator is notified when the timing mode is active.
Such indicators frequently include additional mechanisms for blinking the
LED at a rate depending on the time remaining in the cycle, further
notifying the operator of the condition or state of the timing circuit.
Electrical components of the photometer (FIG. 3) include light emitting
diode (LED) 40, operational amplifier 42, resistor 44 and analog to
digital (A/D) converter 46. In this circuit the LED is reverse biased by
the offset voltage of the operational amplifier and operates as an
inexpensive sensor. As mentioned above in connection with the timing
circuit, the LED is located at 30 (FIG. 4) on the front of the camera
where it intercepts light reflected from the scene. Light impinging on the
LED 40 produces a current that is amplified by the operational amplifier
and feed back resistor 44. The operational amplifier 42 also serves to
isolate the LED from the load, maintaining the linearity of the LED
response to scene illumination. The output of the amplifier 42 is then
converted to a digital exposure control signal by analog to digital
converter 46.
The preferred embodiment is intended for low cost applications, and
therefor does not include additional components for optimizing its
operation in the photometer mode. It should be understood, however, that
other elements might be added within the scope of the invention. Examples
include optical elements for better focusing the scene illumination onto
the LED 40, and electrical elements for calibrating the output of the LED
when it is used as a sensor.
The circuits of FIGS. 2 and 3 are combined in FIG. 1 with switching
elements 48 and 50. In this embodiment, the timing circuit is operated
first with switching elements 48 and 50 engaging contacts 52 and 54,
respectively. Then, when the timer completes its cycle and initiates the
exposure cycle, elements 48 and 50 are switched to contacts 56 and 58,
respectively, to measure scene illumination. In simple cameras the
photometer circuit might simply determine when supplemental flash
illumination is required. In more sophisticated systems, the photometer
circuit might also be used to set the camera aperture, time the camera
shutter, quench the flash and determine other parameters dependent on
scene illumination.
Although the first circuit 14 is depicted in this preferred embodiment as a
timer, and the emitter is used as an indicator, other alternatives
certainly are within the scope of the invention. Examples include
illumination circuits for reducing red eye or for rangefinding. The second
circuit preferably is part of a photometer for adjusting exposure
conditions, but again, other sensors and sensing circuits within the scope
of the invention will become apparent from this description to those
skilled in the pertinent arts. The preferred embodiment has been depicted
with circuits having discrete interconnected components, but other
embodiments of the invention include micro controllers and processors
having programs for carrying out the described functions. Such automated
operation might be particularly advantageous for switching elements 48 and
50. The claims should by interpreted to fairly cover all such
modifications and applications within the true spirit and scope of the
invention.
______________________________________
PARTS LIST FOR FIGURES
Reference No. Part
______________________________________
10 Camera.
12 Optoelectronic Device.
14 First (timing) circuit.
16 Second (photometer) circuit.
18 Optical and exposure system.
20 Electronic flash device.
22 Photoflash tube.
24 Viewfinder.
26 Shutter release.
28 Timer actuation switch.
30 Indicator.
34 Mode transistor.
36 Battery.
38 Resistor.
40 Light Emitting Diode (LED).
42 Operational amplifier.
44 Resistor.
46 Analog to digital (A/D) converter.
48 First switching element.
50 Second switching element.
52 Contact.
54 Contact.
56 Contact.
58 Contact.
______________________________________
Top